下载管理器完成多次下载后如何执行任务

Question

i need to download multiple images when my application starts up. I'm able to download the images properly but the problem im facing is how do i perform a task like move to another activity(where the pics are displayed) or in this case( for testing purposes) change the text of a textview once ALL the downloads are complete. In my code it changes the text view even if one download is complete,which is not what i want. How do i achieve this?

public class MainActivity extends ActionBarActivity {
TextView testtv;
String[] imagenames;
String BASEURL;
private long enqueue;
private DownloadManager dm = null;

@TargetApi(Build.VERSION_CODES.GINGERBREAD)
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    BASEURL = getResources().getString(R.string.base_URL);
    imagenames = getResources().getStringArray(R.array.pic_name);
    testtv = (TextView) findViewById(R.id.testtv);
    File Path = getExternalFilesDir(null);
    File noMedia = new File(Path + "/.nomedia");
    if (!noMedia.exists()) {
        try {
            noMedia.createNewFile();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    Path.mkdirs();
    for (int index = 0; index < imagenames.length; index++) {
        File image = new File(Path + "/" + imagenames[index]);

        if (image.exists()) {
            testtv.setText("file exists");
        } else {
            Boolean result = isDownloadManagerAvailable(getApplicationContext());
            if (result) {
                downloadFile(imagenames[index]);
            }
        }

    }

}

@SuppressLint("NewApi")
public void downloadFile(String imagename) {
    // TODO Auto-generated method stub
    String DownloadUrl = BASEURL + imagename;
    DownloadManager.Request request = new DownloadManager.Request(
            Uri.parse(DownloadUrl));
    request.setDescription("P3 Resources"); // appears the same
                                            // in Notification
                                            // bar while
                                            // downloading
    request.setTitle("P3 Resources");
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
        request.allowScanningByMediaScanner();
        request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE);
    }
    String fileName = DownloadUrl.substring(
            DownloadUrl.lastIndexOf('/') + 1, DownloadUrl.length());
    request.setDestinationInExternalFilesDir(getApplicationContext(), null,
            fileName);

    // get download service and enqueue file
    dm = (DownloadManager) getSystemService(Context.DOWNLOAD_SERVICE);
    enqueue = dm.enqueue(request);

}

public static boolean isDownloadManagerAvailable(Context context) {
    try {
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.GINGERBREAD) {
            return false;
        }
        Intent intent = new Intent(Intent.ACTION_MAIN);
        intent.addCategory(Intent.CATEGORY_LAUNCHER);
        intent.setClassName("com.android.providers.downloads.ui",
                "com.android.providers.downloads.ui.DownloadList");
        List<ResolveInfo> list = context.getPackageManager()
                .queryIntentActivities(intent,
                        PackageManager.MATCH_DEFAULT_ONLY);
        return list.size() > 0;
    } catch (Exception e) {
        return false;
    }
}

private BroadcastReceiver receiver = new BroadcastReceiver() {
    @TargetApi(Build.VERSION_CODES.GINGERBREAD)
    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        if (DownloadManager.ACTION_DOWNLOAD_COMPLETE.equals(action)) {
            long downloadId = intent.getLongExtra(
                    DownloadManager.EXTRA_DOWNLOAD_ID, 0);
            Query query = new Query();
            query.setFilterById(enqueue);
            Cursor c = dm.query(query);
            if (c.moveToFirst()) {
                int columnIndex = c
                        .getColumnIndex(DownloadManager.COLUMN_STATUS);
                if (DownloadManager.STATUS_SUCCESSFUL == c
                        .getInt(columnIndex)) {
                    testtv.setText("Download Complete");

                }
            }
        }
    }
};

@TargetApi(Build.VERSION_CODES.GINGERBREAD)
public void onResume() {
    super.onResume();

    registerReceiver(receiver, new IntentFilter(
            DownloadManager.ACTION_DOWNLOAD_COMPLETE));
}
}

Answer 1

You're currently only storing the last id returned from the DL manager. Changed this to a thread-safe queue - that should fix it if I understand your use can correctly.

public class MainActivity extends ActionBarActivity {
TextView testtv;
String[] imagenames;
String BASEURL;
private Queue<Long> enqueue = new ConcurrentLinkedQueue<>(); 
private DownloadManager dm = null;

@TargetApi(Build.VERSION_CODES.GINGERBREAD)
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    BASEURL = getResources().getString(R.string.base_URL);
    imagenames = getResources().getStringArray(R.array.pic_name);
    testtv = (TextView) findViewById(R.id.testtv);
    File Path = getExternalFilesDir(null);
    File noMedia = new File(Path + "/.nomedia");
    if (!noMedia.exists()) {
        try {
            noMedia.createNewFile();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    Path.mkdirs();
    for (int index = 0; index < imagenames.length; index++) {
        File image = new File(Path + "/" + imagenames[index]);

        if (image.exists()) {
            testtv.setText("file exists");
        } else {
            Boolean result = isDownloadManagerAvailable(getApplicationContext());
            if (result) {
                downloadFile(imagenames[index]);
            }
        }

    }

}

@SuppressLint("NewApi")
public void downloadFile(String imagename) {
    // TODO Auto-generated method stub
    String DownloadUrl = BASEURL + imagename;
    DownloadManager.Request request = new DownloadManager.Request(
            Uri.parse(DownloadUrl));
    request.setDescription("P3 Resources"); // appears the same
                                            // in Notification
                                            // bar while
                                            // downloading
    request.setTitle("P3 Resources");
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
        request.allowScanningByMediaScanner();
        request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE);
    }
    String fileName = DownloadUrl.substring(
            DownloadUrl.lastIndexOf('/') + 1, DownloadUrl.length());
    request.setDestinationInExternalFilesDir(getApplicationContext(), null,
            fileName);

    // get download service and enqueue file
    dm = (DownloadManager) getSystemService(Context.DOWNLOAD_SERVICE);
    enqueue.offer(dm.enqueue(request));

}

public static boolean isDownloadManagerAvailable(Context context) {
    try {
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.GINGERBREAD) {
            return false;
        }
        Intent intent = new Intent(Intent.ACTION_MAIN);
        intent.addCategory(Intent.CATEGORY_LAUNCHER);
        intent.setClassName("com.android.providers.downloads.ui",
                "com.android.providers.downloads.ui.DownloadList");
        List<ResolveInfo> list = context.getPackageManager()
                .queryIntentActivities(intent,
                        PackageManager.MATCH_DEFAULT_ONLY);
        return list.size() > 0;
    } catch (Exception e) {
        return false;
    }
}

private BroadcastReceiver receiver = new BroadcastReceiver() {
    @TargetApi(Build.VERSION_CODES.GINGERBREAD)
    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        if (DownloadManager.ACTION_DOWNLOAD_COMPLETE.equals(action)) {
            long downloadId = intent.getLongExtra(
                    DownloadManager.EXTRA_DOWNLOAD_ID, 0);
            if (enqueue.contains(downloadId)) {
                enqueue.remove(downloadId);
            }

            if (!enqueue.isEmpty()) {
                return;
            }

            //not waiting on any more downloads
            testtv.setText("Downloads Complete");
        }
    }
};

@TargetApi(Build.VERSION_CODES.GINGERBREAD)
public void onResume() {
    super.onResume();

    registerReceiver(receiver, new IntentFilter(
            DownloadManager.ACTION_DOWNLOAD_COMPLETE));
}
}

Answer 2

First of all I must say that it sounds like you shouldn't be using download manager at all.

If you want to download images and display them, odds are you should just use HTTPUrlConnection or similar and do it that way.

That said, there are several ways to achieve what you want.

Java Futures is one approach. RxJava might be a good choice.

Heck, just adding expected results to an array and iterating through that in onReceive will work.